Method and device for monitoring a flexible pipe

ABSTRACT

A device for monitoring the integrity of a flexible pipe used for transporting a pressurized fluid in a terminal end-fitting. The pipe includes an internal pressure sheath, plies of tensile armor wires and an outer sheath fastened to the end-fitting. A device monitors the change in a phenomenon associated with a failure of the armor plies as a result of a fracture of several tensile armor wires inside the end-fitting. The device detects an increase in the twist in the pipe near the end-fitting, which twist is a phenomenon of a fracture of tensile armor wires inside the end-fitting.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a 35 U.S.C. §§ 371 national phase conversionof PCT/FR2003/002694 filed 11 Sep. 2003, which claims priority of FrenchApplication No. 02/11556 filed 18 Sep. 2002. The PCT InternationalApplication was published in the French language.

BACKGROUND OF THE INVENTION

The present invention relates to a method of monitoring a flexible pipefor transporting, over long distances, a fluid that is under pressureand possibly at a high temperature, such as a gas, oil, water or otherfluids. The invention relates more particularly to the monitoring andwarning of problems associated with a fracture of the armor wires of theflexible pipe in the vicinity of or inside the terminal end-fitting,where they are anchored, especially in a terminal end-fitting for arising flexible pipe, called a “riser”, intended for offshore oilproduction. The present invention also relates to a device associatedwith the monitoring method.

Flexible pipes used offshore have various configurations depending ontheir precise use, but in general they satisfy the constructionalcriteria defined in particular in the API 17 B and API 17 J standardsdrawn up by the American Petroleum Institute under the title“Recommended Practice for Flexible Pipe” and “Specification for UnbondedFlexible Pipe”. These pipes comprise, from the inside outward:

an internal sealing sheath or pressure sheath, made of a plastic,generally a polymer, resistant to the chemical action of the fluid to betransported;

optionally, a pressure vault resistant mainly to the pressure developedby the fluid in the sealing sheath and consisting of the winding of oneor more interlocked metal profiled wires, which may or may not beself-interlockable, that are wound in a helix with a short pitch (i.e.with a lay angle of close to 90°) around the internal sheath; theprofiled wires have a cross section in the form of a Z or a T or theirderivatives (teta® or zeta), or in the form of a U or an I; the saidpressure vault may also include a hoop;

at least one ply (and generally at least two crossed plies) of tensilearmor plies wound with a long pitch, the lay angle measured along thelongitudinal axis of the pipe being less than 60°; and

an external protective sealing sheath made of a polymer.

Such a pipe may have a smooth internal bore, when the bore is formeddirectly by the sealing sheath (the pipe is then called a smooth borepipe) or may have a rough bore, when a carcass consisting, for example,of an interlocked metal strip serving to prevent the pipe fromcollapsing under the external pressure is furthermore provided insidethe internal sealing sheath.

The end-fittings for the pipes, which are intended for connecting themtogether or to terminal equipment, are also defined in the API 17 Jrecommendations and must be produced under conditions ensuring both goodfastening and good sealing. They are generally obtained by crimping thesheath, that is to say by the partial radial penetration of a rigidelement into the sheath.

Several types of end-fittings for flexible pipes using the principle ofcrimping the internal sheath are known, especially from documents FR 2214 852 or WO 99/19655, or else from document WO 97/25564 in the name ofthe Assignee hereof, and document PCT/FR01/03305 also in the name of theAssignee. The latter document describes in particular a fasteningend-fitting for a flexible tubular pipe, comprising a first annularportion (generally called the vault of the end-fitting) to which maybear a first crimping flange provided with a cone for crimping theinternal sheath and a second annular portion (generally called a cap)which surrounds, and extends rearwards, the first annular portion and onwhich a second crimping flange can bear. The second crimping flange isprovided with a cone for crimping the external sheath, cooperating witha rear crimping support sleeve. The second annular portion defines withthe first annular portion an annular space in which the tensile armorplies are placed in such a way that they are radially separate from theinternal sheath so as to pass around the first crimping flange and thefirst annular portion in order to be fastened thereto. The end-fittingincludes a collar for immobilizing the armor wires between the firstcrimping flange and the second crimping flange. The aforementionedannular space is intended to be filled with a filling material such as aresin which will immobilize the various elements lying in this space.

It is known to monitor the integrity of a pipe and a pipe end-fittingover time using various methods and devices for the purpose of detectingcertain anomalies.

Thus, methods are known for inspecting the inside of a pipe, using aninspection “pig” traveling along the pipe and giving, for example, videoimages or identifying a possible retraction of the carcass at anend-fitting by an eddy current system and associated sensors (see FR 2790 087 in the name of the Assignee). Besides the fact that such methodsgive information about the carcass but not directly about the sheath (inthe case of rough bore pipes), they have a drawback of requiringproduction to be temporarily stopped in order to send the pig into thepipe.

Methods are also known for detecting leaks in pipes (FR 2 626 974 andU.S. Pat. No. 4,775,855) or for detecting the imminent fracture of apipe using sensor elements placed on the pipe (GB 2 057 696).

Methods have also been developed that are more specifically associatedwith the monitoring of end-fittings because it has been noted that theseare the site of certain types of deterioration over time. It is usefulto be able to detect in time such deterioration in order to be able tointervene in a programmed manner on the pipe and on the end-fitting, andto carry out the necessary repairs or replacements.

In particular, it is known and recommended to monitor the position ofthe pressure sheath by regular inspection.

To be able to obtain sheath displacement information effectively, it hasbeen proposed in document WO 98/12545 to provide markers on the elementto be monitored, the displacement of which markers can be detected byX-rays using an X-ray detector or an X-ray sensitive photographic film.In all cases, this requires heavy equipment and also requires productionto be stopped in order to be able to place the detector around the pipe.

The Assignee has also proposed, in French application No. 02/02155, adetection method and an associated end-fitting that can provideinformation about the displacement of the pressure sheath or of otherlayers of the pipe without having to stop production. The end-fitting issuitable for detection, because it is equipped directly with a sensorfor detecting the displacement of a given layer in the pipe, especiallythe pressure sheath.

Document U.S. Pat. No. 3,972,223 relates to a method and to a device formonitoring the integrity of a pipe over its length or over the length ofeach of its sections. The document provides for elongate bladders to beplaced in the thickness of the multilayer wall of the pipe, saidbladders being filled with a pressurized fluid and communicating viatubes with one or more pressure gauges. Any impact along the length ofthe pipe, or destruction of the layers of the wall of the pipe, resultsin variations of the pressure of the fluid contained in the bladders,these being detected by the pressure gauge or gauges. However, thatdocument does not in any way show that this method can be used formonitoring the end-fittings themselves.

Document GB 2 148 447 shows a connection end-fitting. An annular spacelying between two armor plies experiences its pressure measured using apressure gauge, to which the annular space is connected via a bore. Thispressure gauge can detect anomalies in the leakage rate that mayindicate damage of the armor plies, this damage not necessarily beinglocated in the end-fitting. That document therefore does not teachmonitoring in the terminal end-fitting either.

All these monitoring methods help as far as possible to preventproduction incidents in the pipe. However, in certain causes ofimpairment to the flexible pipe the end-fitting cannot be detected bythe existing method. This is especially the case as regards the fractureof certain of the wires forming the tensile armor plies. Such fractureof the wires, which is progressive over time, may result in destructionof the end-fitting and therefore of the pipe when the number of wiresdamaged increases. Thus, the present invention is aimed at improving themonitoring of the terminal end-fittings of flexible pipes so as toprevent sudden production stoppages. It essentially consists inmonitoring, and giving warning about, potential incidents relating tothe integrity of the wires of the tensile armor plies inside theend-fitting.

SUMMARY OF THE INVENTION

The invention achieves its objective thanks to a method of monitoringthe integrity of a flexible pipe for transporting a pressurized fluid ina terminal end-fitting. The pipe comprises, in particular, an internalpressure sheath, plies of tensile armor wires and an outer sheathfastened to the end-fitting. The method comprises monitoring theintegrity of the tensile armor plies in the end-fitting by monitoringthe change in the twist in the flexible pipe as a phenomenon associatedwith the disorganization of the armor plies as a result of fracture ofseveral tensile armor wires inside the end-fitting. To the knowledge ofthe Applicant, it has never previously been proposed to monitor theintegrity of the armor plies in the pipe end-fitting, nor have thephenomena warning of the failure of the tensile armor plies, especiallythe twist in the pipe, ever been examined.

Thus, according to the invention, to monitor the integrity of the armorplies, the twist in the flexible pipe near the end-fitting is monitored,for example by means of strain gauges, especially one or moreextensometric gauges. These gauges may especially be placed on or incontact with the external sheath of the pipe, near the terminalend-fitting. This is because breakage of the armor wires in theend-fitting results in an imbalance in the forces and tensions in thesuperposed plies, resulting in a twist in the pipe. This twist thus hasa tendency to adopt a “corkscrew” or “pig-tail” form near theend-fitting where the break of the armor wires occurs and it is thistwist or at least its progressive appearance that can be monitoredaccording to this first embodiment.

It is advantageous to combine this twist detection with the monitoringof one or more parameters associated with the escape of gas at theend-fitting, and more precisely at one of the discharge valves providedin the end-fitting and more commonly called gas drainage valves. This isbecause when the flexible pipe is transporting a fluid containing gases(a polyphase fluid), certain gases diffuse into the annulus between thepressure sheath and the outer sheath. These gases are drained away inthe annulus to the end-fittings where they are discharged via thesevalves (generally three in number in the end-fittings). The fracture ofthe armor wires in the end-fitting results in an elongation of the pipeswhich stresses the sealing sheath to the point of inducing fracture inthe sealing barrier for the internal bore of the pipe and thereforeincreases the gas flow in the annulus. This additional construction cantherefore be used in hydrocarbon production risers or gas lift risers,but not on water injection risers. Escape of gas can be monitored bymeasuring one or more parameters associated with gas escape, such as thedischarge frequency and/or discharge time and/or output of the valve,for example.

It is possible, and even recommended, to combine the two monitoringsystems in order to increase the certainty of detection.

From the occurrence of an anomaly during the monitoring, it may beconcluded that the integrity of the tensile armor plies has suffered dueto the fracture of several of the constituent wires and thus givingwarning about the risk of an imminent fracture of the pipe at theend-fitting, so as to take the necessary measures for protecting andsafeguarding the pipe.

The invention also relates to the device associated with the method ofthe invention. This device for monitoring the integrity of a flexiblepipe for transporting a pressurized fluid at a terminal end-fitting,said pipe comprises in particular an internal pressure sheath, plies oftensile armor wires and an outer sheath that are fastened to theend-fitting. It is noteworthy that the device comprises means formonitoring the change in a phenomenon due to the disorganization of thearmor plies as a result of fracture of several tensile armor wiresinside the end-fitting. These monitoring means are means for detectingan increase in the twist in the pipe near the end-fitting.

Advantageously, the monitoring means include a computing unitresponsible for recovering and analyzing the signal sent by the pipetwist detection means. The same computing unit may serve for monitoringseveral risers that are equipped with said monitoring means and fortriggering an alarm when the detection means have detected an anomaly inone of the pipes being monitored.

BRIEF DESCRIPTION OF THE DRAWING

Other advantages and features will be demonstrated on reading thedescription that follows with reference to the appended FIGURE whichshows schematically a terminal pipe end-fitting, with partial cutaway,equipped with detection means according to the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

The FIGURE shows highly schematically an end-fitting 1 which issymmetric about its longitudinal axis XX′ coincident with the centralaxis of the pipe 2. The end-fitting, partially covered with a stiffener12, includes a connection flange 3 for fastening to a platform 4. Thepipe 2 comprises, as is known, a carcass 5 and its pressure sheath 6,tensile armor plies 7 and an outer sheath 8. These various constituentelements are fastened and crimped to the inside of the end-fitting 1 byvarious means known per se, especially those known from document WO02/39003 or document U.S. Pat. No. 6,039,083. For example, the armorplies may be held in place by collars 7′ and embedded in a resin.Moreover, the gases appearing in the annulus of the pipe 2 are connectedin a line 9 that communicates with the outside via a staged valve 10 orgas drainage valve (only one of the three valves normally present hasbeen shown). A staged differential valve is known, for example fromdocument FR 2 777 966 or document U.S. Pat. No. 2,420,370. Theseelements, which are known per se, do not require to be described infurther detail. Besides, the invention does not depend on the preciseconfiguration of the end-fitting and of the pipe, rather it can beimplemented on other types of end-fitting and on a pipe other than thatillustrated here. The description of the end-fitting is given merely byway of indication of one possible embodiment in which the invention canbe implemented and likewise the flexible pipe may have a differentinternal structure with regard to the number of constituent layers andtheir nature.

In the method according to the invention for monitoring the integrity ofthe armor wires 7 or their anchoring in the end-fitting, the twistliable to be generated in the pipe because of the disorganization of thearmor plies is monitored, it being possible for said twist to bedetected in the sheath 8 of the pipe 2, near the end-fitting 1. To dothis, the flexible pipe 2 is equipped with linear extensometers orgauges designed to detect the twists in the pipe. These gauges may, forexample, take the form of a rod 20 (commonly called a “Smart Rod®”)which is equipped with Bragg grating optical fibers. The pipe 2 may thusbe equipped with one or more rods 20, each having several strain gaugesand intended to deliver, to the analysis device 23 to which they areconnected, information about the shape adopted by the flexible pipe 2near the end-fitting. The positioning of the rod or rods and theirnature depend essentially on the conditions under which the pipe isbeing used and on the desired detection sensitivity. In the exampleillustrated in FIG. 1, the monitoring device comprises a rod 20 mountedso as to slide in collars 21, there being three of said collars, spacedapart respectively by a distance A (the pitch of the external armor ply)and by a half-pitch A/2. This rod 20, which is equipped withextensometers (of the Bragg grating type) provides information about itsflexure in each of the gaps between the collars 21, from whichinformation it is possible to deduce whether or not there is a twist inthe pipe 2. The number of rods needed to monitor a pipe and how they areinstalled along the sheath 8 near the end-fitting 1 essentially dependson the fine detail of the information needed for the monitoring. This orthese rods 20 are connected by a connection 22 to the analysis device 23which, by comparison with a given threshold, makes it possible to detectan abnormal twist of the pipe 2 and will generate an alarm that allowsthe user to anticipate the breakage of the flexible pipe at its terminalend-fitting and therefore to plan a production shutdown and theappropriate maintenance operations. This twist, detected by theextensometry sensors of the rod(s) 20, is a manifestation of a failurein the integrity of the wires of the armor plies 7.

The principle of linear gauges is well known, especially in the form ofBragg grating optical fibers. The reader may refer to documents FR 2 791768 and WO 99/32862.

The computing unit 24, which constitutes the core of the analysis device23, connected to the linear gauges located on the rod 20 is programmedto make a distinction between localized or transient deformations of thepipe, associated with its operating conditions (swell, current, etc.)and the permanent deformations that are symptomatic of a twist in thepipe 2 associated with failure of the tensile armor plies 7 inside theterminal end-fitting 1.

The FIGURE shows a rod 20 provided with linear gauges, this rod beingplaced on the outside of the pipe and even partly above the stiffener,this being more convenient in order to place the monitoring device on anexisting installation. If the monitoring device is provided right fromthe beginning, it is possible to incorporate it between the stiffenerand the external sheath of the pipe. It is also possible to integratethe detection means (the linear gauges, etc.) actually on the inside ofthe pipe, such as within the armor plies or elsewhere in the pipe nearthe end-fitting.

Of course, twist detection means other than extensometric gauges arepossible.

In particular, it is possible to combine a twist detection that has justbeen applied with detection of a variation in the parameters associatedwith the exhausting of the drained gas in the annulus of the pipe 2.This exhausting takes place in one of the gas drainage valves 10 thatare located in the terminal end-fitting 1. This monitoring is performedby means of a device comprising detection means 25 (for example pressureswitches) connected to an analysis device 23 that can generate an alarmwhen variation in the frequency, in the flow rate or the discharge time,or even the pressure within the annulus, is symptomatic of a tensilearmor ply failure problem. In fact such a failure involves progressiveloss of sealing of the internal sheath at the point where it is crimpedin the end-fitting, increasing the gas flow inside the internal sheathtowards the annulus and therefore substantially modifying the parametersassociated with exhausting the gas. The detection means 25 may be formedby pressure sensors or flow rate sensors that can deliver, in real time,to the analysis device (the computing unit) information associated withthis exhausting of the drained gases. These sensors 25 may also measureall types of parameters associated with this exhausting, parameterswhich make it possible to deduce that there is a significant increase inthe volume of gas drained to the outside through the gas draining valve10. Thus, the sensors may measure the volume of drained gas directly ormay measure the discharge frequency of the valve or even the time duringwhich said valve is open, for example. The sensors 25 measure, forexample, the discharge frequency and the computing unit 24 makes acomparison over the last five discharges in order to obtain therefrominformation about a possible increase in the frequency associated with afailure of the tensile armor plies.

This method of monitoring the integrity of a flexible pipe in itsterminal end-fitting and especially of a riser-type pipe (i.e. a pipeconnecting sub-sea equipment to a surface installation) and theassociated detection devices are advantageously applicable in existingoffshore oil production systems, without which a plurality of risers isused. This is because each riser can be provided with detection means ofthe type described above, these means being intended to monitor thetwist in the flexible pipe and optionally the discharge of the gases ina discharge valve of the end-fitting. All of said detection means arethen connected to a common analysis device which allows the signalsreceived to be analyzed in order to generate, if necessary, an alarmshould a failure be detected in one or more tensile armor plies inside aterminal end-fitting of one of the risers.

1. A method of monitoring integrity of a flexible pipe used fortransporting a pressurized fluid in a terminal end-fitting of theflexible pipe, wherein the flexible pipe comprises at least an internalpressure sheath, plies of tensile armor wires and an outer sheathfastened to the end-fitting, the method comprising: monitoring theintegrity of the tensile armor plies of the flexible pipe in theend-fitting by detecting a change in a twist in the flexible pipeadjacent the end-fitting, wherein the twist change is a phenomenonassociated with a failure of the armor plies as a result of a fractureof two or more tensile armor wires inside the end-fitting.
 2. The methodas claimed in claim 1, wherein the monitoring of the change in the twistin the flexible pipe is by at least one strain gauge placed on theexternal sheath of the pipe.
 3. The method as claimed in claim 1,wherein the end-fitting includes a gas drainage valve, and themonitoring of the integrity comprises monitoring the quantity of gasescaping from the valve.
 4. The method as claimed in claim 3, whereinthe monitoring of the quantity of gas escaping comprises measuring avariation in at least one of a discharge frequency and in a dischargetime of the gas.
 5. A device for monitoring the integrity of a flexiblepipe for transporting a pressurized fluid at a terminal end-fitting ofthe pipe, the pipe comprising at least an internal pressure sheath,plies of tensile armor wires and an outer sheath fastened to theend-fitting, the device for monitoring the integrity comprising: amonitoring device operable for detecting a failure of the armor plies asa result of a fracture of two or more tensile armor wires inside theend-fitting, the monitoring device being operable to detect the failureby detecting an increase in a twist in the flexible pipe adjacent theend-fitting.
 6. The device as claimed in claim 5, wherein the monitoringdevice for detecting an increase in the twist in the pipe comprisesstrain gauges at the pipe.
 7. The device as claimed in claim 6, whereinthe strain gauges comprise Bragg grating optical fibers.
 8. The deviceas claimed in claim 5, wherein the monitoring device includes acomputing unit operable to generate an alarm depending on anomalies themonitoring device detects.